Synthesis,crystal structure and properties of a copper(II) complex with the tripod ligand tris ( N -methylbenzimidazol-2-ylmethyl)amine and 4-hydroxycinnamate

A five-coordinate copper complex with the tripod ligand tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) and 4-hydroxycinnamate, with the composition [Cu(Mentb)(4-hydroxycinnamate)](ClO₄)?·?0.5DMF, was synthesized and characterized by means of elemental analyses, electrical conductivities, thermal analyses, IR, and UV. The crystal structure of the copper complex has been determined by single-crystal X-ray diffraction, and shows that the Cu^II atom is bonded to a tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) ligand and a 4-hydroxycinnamate through four N atoms and one O atom, giving a distorted trigonal-bipyramidal coordination geometry (τ?=?0.78), with approximate C₃ molecular symmetry. Cyclic voltammograms of the copper complex indicate a quasireversible Cu⁺²/Cu⁺ couple. Electron spin resonance data confirm the trigonal–bipyramidal structure and indicate g _∥?<?g _⊥ with a very small value of A _∥ (57?×?10^?4?cm^?1).     

Synthesis,crystal structure and properties of a novel copper(II) complex with tripod ligand tris(1H-benzimidazol- 2-ylmethyl)amine

A five-coordinate copper complex with the tripod ligand tris(1H-benzimidazol-2-ylmethyl)amine (ntb), of composition [Cu(ntb)(H₂O)] (C1O₄)₂?·?C₅H₄N₂O₃?·?H₂O (C₅H₄N₂O₃?=?4-nitropyridine-N-oxide), was synthesized and characterized by means of elemental analyses, electrical conductivities, thermal analyses, IR, and U.V. The crystal structure of the copper complex has been determined by single-crystal X-ray diffraction, and shows that the Cu^II is bonded to a tris(1H-benzimidazol-2-ylmethyl)amine (ntb) ligand and a water molecule through four N atoms and one O atom, giving a distorted trigonal–bipyramidal coordination geometry with approximate C ₃ molecular symmetry. Cyclic voltammograms of the copper complex indicate a quasi-reversible Cu⁺²/Cu⁺ couple. Electron spin resonance data confirm a trigonal-bipyramidal structure and with g ₂?<?g _ζ and a very small value of A ₂ (20?×?10^?4?cm^?1).     

The determination of oxygen in copper by α-particle activation analysis

The determination of oxygen in copper by activation analysis with 45-MeV α-particles is described. The chemical separation of ¹⁸F produced from oxygen consists of steam distillation as fluosilicic acid, followed by precipitation of the interfering gallium activities as the hydroxide and of the fluoride as lead chlorofluoride or of cation exchange followed by lead chlorofluoride precipitation. This allows a total decontamination from matrix radiation in excess of 10⁶. As standard, mica foils are used, while, for the purp?ose of flux monitoring, the activity induced in a thin copper or mica foil, placed before the sample is counted. Alternatively, the intensity of the particle beam is measured. The method, which allows determination of oxygen at the 1 μg g^-1 level with a precision of about 10%, is applied to the determination of a concentration of 1.2 μg g^-1. Analysis of a reference material containing 70 μg O g^-1 proves the accuracy of the standardization methods applied.     

Chemistry of copper trimercaptotriazine (TMT) compounds and removal of copper from copper‐ammine species by TMT

The acid dissociation constants of 2,4,6‐trimercaptotriazine (H₃TMT) were determined by acid‐base titration and now can be employed in the preparation of complexes having specific Cu–TMT ratios. IR, EA and TGA characterized the compounds. We analyzed the relevant IR spectra and attribute 2910–2925, 3030–3250 and 3430 cm^?1 to triazine ring overtone, N? H stretching vibrations and water in the TMT complexes, respectively. The solubility of Cu–TMT complexes was determined with ICP‐AES. The results indicate that Cu₃ (TMT)₂ · 2H₂O ( 3 ) is much more insoluble and more stable than Cu (H₂TMT)₂ ( 1 ), Cu (HTMT)·0.5H₂O ( 2 ) and CuS. The extremely small value of K_SP for compound 3 (2.11 × 10^?46) indicates that Na₃TMT is a very advantageous chelating agent in precipitating complex copper (e.g. copper‐ammine species) from industrial wastewaters. The influences of ammonia concentration, pH and settling time on the effectiveness of copper precipitation were investigated. Also, a ‘real world’ printed circuit board factory effluent initially containing 350.9 ppm of Cu was treated and it was found that more than 99.9% of the copper was removed from the solution as an insoluble compound 3 . Copyright © 2006 John Wiley & Sons, Ltd.     

Reduction from copper(II) to copper(I) upon collisional activation of (pyridine)2CuCl+

Electrospray ionization of dilute aqueous solutions of copper(II) chloride‐containing traces of pyridine (py) as well as ammonia permits the generation of the gaseous ions (py)₂Cu⁺ and (py)₂CuCl⁺, of which the latter is a formal copper(II) compound, whereas the former contains copper(I). Collision‐induced dissociation of the mass‐selected ions in an ion‐trap mass spectrometer (IT‐MS) leads to a loss of pyridine from (py)₂Cu⁺, whereas an expulsion of atomic chlorine largely prevails for (py)₂CuCl⁺. Theoretical studies using density functional theory predict a bond dissociation energy (BDE) of BDE[(py)₂Cu⁺ ‐Cl] = 125 kJ mol^?1, whereas the pyridine ligand is bound significantly stronger, i.e. BDE[(py)CuCl⁺ ‐py] = 194 kJ mol^?1 and BDE[(py)Cu⁺ ‐py] = 242 kJ mol^?1. The results are discussed with regard to the influence of the solvation on the stability of the Cu^I/Cu^II redox couple. Copyright © 2010 John Wiley & Sons, Ltd.     

Unusual electrochemical reduction of copper(II) to copper(I) in polyoxotungstates

The electrochemical behaviour of the copper-substituted Keggin-type and sandwich-type polyoxotungstate anions of the compounds α-[(C₄H₉)₄N]₄H[PW₁₁Cu^IIO₃₉] and α-B-[(C₄H₉)₄N]₇H₃[Cu^II₄(H₂O)₂(PW₉O₃₄)₂] was studied by cyclic voltammetry in acetonitrile. In both cases two copper 1-electron reduction waves were detected in the cathodic scan. The first one was due to the reduction of one Cu^II to Cu^I in the polyoxoanion and the second one to the consecutive reduction of the preformed Cu^I to Cu⁰, with the consequent deposition/adsorption of the ejected metal atom at the glassy carbon electrode surface. In the anodic scan, Cu⁰ was re-oxidised with regeneration of the initial copper(II) complexes, via a Cu^I intermediate. The observed two-step reduction of copper(II) to copper(0) and the formation of intermediate species containing copper(I) is here reported for the first time for copper substituted polyoxotungstates. The co-ordination of the acetonitrile molecules to the copper ions must play a role in the formation of the copper(I) species, which are not detected in aqueous solution.     

Determination of Cr(VI) in plants by electrothermal atomic absorption spectrometry after leaching with sodium carbonate

The determination of chromium (VI) compounds in plants by electrothermal atomic absorption spectrometry (ET AAS) is proposed based on their leaching with 0.1 M Na₂CO₃. Due to the presence of relatively high amounts of Na₂CO₃ in the resulting samples, the temperature and time of pyrolysis and atomization stages must be optimized to minimize the influence of the matrix. A limit of detection (LOD) for determination of Cr(VI) in plants by ET AAS was found to be 0.024 μg g⁻¹.The concentration of Cr(VI) and total chromium in plants collected in different geographical areas (South Africa and Russia), grown on soils high in chromium was determined. The concentration of Cr(VI) and total Cr in stems and leaves of plants was in the range of 0.04–0.7 μg g⁻¹ and 0.5–10 μg g⁻¹, respectively. The limited uptake of Cr(III) by plants, in comparison to its concentration in soil, can be explained by the very low solubility of natural Cr(III) compounds.Results for the determination of Cr(VI) were confirmed by the analysis of BCR CRM 545 (Cr(VI) in welding dust) with good agreement between certified (39.5 ± 1.3 μg mg⁻¹) and found (38.8 ± 1.2 μg mg⁻¹) values. The total concentration of Cr in plants has also been determined by ET AAS after dry ashing of samples at 650 °C. Results were confirmed by the analysis of BCR CRM 281 (Trace elements in Rye Grass) with good agreement between the found (2.12 ± 0.16 μg g⁻¹) and certified value (2.14 ± 0.12 μg g⁻¹).     

Determination of bismuth,lead and tellurium in copper by atomic absorption spectrometry with introduction of solid samples into an induction furnace

Atomic absorption spectrometry with an induction furnace is used for the determination of bismuth (0.015–10 μg g^-1), lead (0.2–15 μg g^-1) and tellurium (0.04–5 μg g^-1) in 2–30-mg samples of copper and low-alloy copper dropped into the furnace. Calibration graphs of peak area versus mass of element were constructed by use of standardised alloys. The accuracy, precision and limits of detection of the method are described for numerous copper samples. With alloys containing more than 0.1 μg Bi g^-1, 0.2 μg Pb g^-1 and 0.8 μg Te g^-1, average relative standard deviations are 7%, 6% and 8%, respectively. The limits of detection for bismuth, lead and tellurium are 0.01, 0.1 and 0.02 μg g^-1, respectively.     

A five-coordinate copper(II) perchlorate complex with tris(N-methylbenzimidazol-2-ylmethyl)amine and salicylate

A five-coordinate copper(II) complex with the tripod ligand tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) and salicylate, with the composition [Cu(Mentb) (salicylate)](ClO₄) · 2DMF, was synthesized and characterized by elemental and thermal analyses, electrical conductivity, IR and UV-Vis spectral measurements. The crystal structure of the complex has been determined by single-crystal X-ray diffraction. The Cu(II) is five-coordinate with four N atoms from the Mentb ligand and an O atom of the monodentate salicylate ligand. The N₄O donors are in a distorted trigonal-bipyramid geometry. Cyclic voltammograms indicate a quasireversible Cu²⁺/Cu⁺ couple. The X-band EPR spectrum of the complex confirms the trigonal-bipyramidal structure with g_∥ < g _⊥ and a very small value of A_∥ (41 × 10^?4 cm^?1).     

Effect of six triorganotin(IV) compounds on nitrification and ammonification in soil

The effects of six triorganotin(IV) compounds and of Thiram on nitrification and ammonification in soil were investigated. Low concentrations of up to 50 μg g^?1 of the triorganotin(IV) compounds enhanced nitrate-nitrogen (NO₃^?-N) production in soil. Except for diphenylbutyltin bromide, which inhibited nitrification at 250 μg g^?1, the other triorganotin(IV) compounds were inhibitory at concentrations of 100 μg g^?1 to less than 250 μg g^?1. At 10 μg g^?1, only triphenyltin acetate was less inhibitory towards nitrification compared with Thiram. At 250 μg g^?1, Thiram exerted a strongly persistent inhibitory effect towards nitrification. The NO₃^?-N level recorded 28 days after application was only 0.10 μg g^?1 soil. With the triorganotin compounds NO₃^?-N levels of 7.05–12.06 μg g^?1 soil were recorded 28 days following their application. The deleterious effects of the triorganotin(IV) compounds were less persistent and recovery of nitrification was evident seven days after application. Low concentrations of Thiram and triorganotin(IV) compounds inhibited ammonification, whereas higher concentrations enhanced ammonification. Complete inhibition of ammonification was attained 21–28 days after application of Thiram at 50 μg g^?1. On the other hand, with the triorganotin(IV) compounds, except for diphenylbutyltin bromide at 10–50 μg g^?1, ammonification persisted at all concentrations 28 days after application.     

Open‐tubular capillary electrochromatography for the simultaneous determination of cadmium and copper in plants

We discuss the separation and determination of cadmium and copper in plant samples such as Triticum durum (wheat) and Helianthus annuus (sunflower) using open tubular capillary electrochromatography with indirect detection. Before performing the analysis, the samples were digested by microwave‐assisted methods using HNO₃. Regarding the electrophoretic system, several experimental parameters were previously evaluated such as the capillary surface, mobile phase composition, buffer, pH, and voltage applied. The baseline resolution of the studied metals was obtained within 8 min by using a capillary immobilized with carboxylic multi‐walled carbon nanotubes and a background electrolyte composed of 6 mM imidazole, pH 4.0. The applied voltage and the temperature were set at 20 kV and 25°C, respectively. Precision, detection, and quantification limits, along with linearity were investigated. The limits of detection and quantification were 2.20 and 7.40 μg/kg, for Cu²? and 0.05 and 0.20 μg/kg in the case of Cd²?. A good linearity was achieved over a concentration working range of 7.5–100 and 0.2–25 μg/kg for Cu²? and Cd²? accordingly. Recovery data for validation studies were found in a range of 98.2–101.5% for both analytes.     

Gas-phase structure and conformational properties of copper (I) pivalate dimer (CuC5H9O2)2

The molecular structure and conformational properties of gaseous dimer of copper (I) pivalate, Cu₂piv₂, have been studied by gas electron diffraction (GED) at 413(5) K and quantum chemical calculations (DFT and MP2). The molecule possesses a planar eight-membered skeleton. Two conformers, “staggered” of C _2h symmetry and “eclipsed” of C _2v symmetry, were found for Cu₂piv₂ in the gas phase. The following geometric parameters of the skeleton ring and the tert-butyl groups have been determined from the GED experiment for the “staggered” form: r_g(Cu···Cu) = 2.520(8) Å, r_g(Cu–O)_ave = 1.871(4) Å, r_g(C–O)_ave = 1.273(3) Å, r_g(C–C)_ring-tert = 1.531(4) Å, r_g(C–C)_{tert-out-of-plane-ring} = 1.536(4) Å, r_g(C–C)_{tert-in-the-plane-ring} = 1.527(4) Å, r_g(C–H)_ave = 1.087(5) Å, (O–Cu–O) = 172.12°(3). Computations predict the internal rotation of the tert-butyl groups to be independent. The value of calculated Wiberg bond index for Cu···Cu testifies the existence of weak bonding between two copper atoms.

     

Determination of copper in zinc by proton activation analysis

A method for the determination of copper in zinc by proton activation analysis using the⁶³Cu(p, n)⁶³Zn reaction has been developed.⁶³Zn has to be separated chemically from gallium and copper activities formed out of the zinc matrix and from indium activity formed out of cadnium impurity. Gallium radionuclides are retained on a cation exchanger in chloride medium and the residual activity is extracted in di-isopropyl ether. Copper and indium are subsequently extracted with cupferron in chloroform. The method was applied to BCR reference materials with a copper concentration at the μg.g^?1 level. The detection limit amounts to 0.5 μg.g^?1.     

Trinuclear copper(II) complexes of some aza macrocycles

The syntheses of copper(II) complexes with neutral macrocyclic ligands 1,4,7,10,12,- 15,17,20,23,26,27,30-dodecaazadispiro[10·4·10·4]triacontane (DDST), 2,5,7,10,13,15,18,21,-23,26,29,32-dodecaazatricyclo[20·10·0·0^6,17]dotriacontane (DOCD) and 2,5,7,10,13,16,18,-21,23,26,29,32-dodecaaza-1,6,17,22-tetrachlorotricyclo[20·10·0·0^6,17]dotriacontane (DTTD) derived from triethylenetetramine, 1,2-diaminoethane and chlorocarbons (carbon tetrachloride, 1,l,2,2-tetrachloroethane and hexachloroethane, respectively) have been studied. Complexes [Cu₃(DDST)]Cl₆, [Cu₃(DOCD)]Cl₆ and [Cu₃(DTTD)]Cl₆?·?H₂O and the copper ion-free ligand hydrochlorides DDST?·?12HCl and DOCD?·?12HCl are supported by elemental analyses, conductivity measurements and spectroscopic studies. Potentiometric equilibrium studies on DDST and DOCD hydrochlorides and their copper complexes also support the structures.     

A Stable Crystalline Copper(I)–N2O Complex Stabilized as the Salt of a Weakly Coordinating Anion

Nitrous oxide is considered a poor ligand, and therefore only a handful of well‐defined metal–N₂O complexes are known. Oxidation of copper powder with an extreme oxidant, [Ag₂I₂][ An ]₂ ([ An ]^?=[Al(OC(CF₃)₃)₄]^?) in perfluorinated hexane leads to Cu^I[ An ], the first auxiliary ligand‐free Cu^I salt of the perfluorinated alkoxyaluminate anion. The compound is capable of forming a stable and crystalline complex with nitrous oxide, Cu(N₂O)[ An ], where the Cu?N₂O bond is by far the strongest among all other molecular metal–N₂O complexes known. Thorough characterization of the compounds together with the crystal structure of Cu(N₂O)[ An ] complex supported with DFT calculations are presented. These give insight into the bonding in the Cu⁺–N₂O system and confirm N‐end coordination of the ligand.     

Atomic absorption spectrometric determination of copper in calcium carbonate scale and carbonate rocks by direct atomization of solid samples

Powdered samples (1 mg) are mixed with 1 mg of powdered graphite and copper is determined by atomic absorption spectrometry in a miniature graphite cup placed in a graphite crucible. Optimum conditions were drying at 200 °C (30 s), ashing at 900 °C (30 s), atomizing at 2700 °C (15 s) and cleaning at 2800 °C (10 s). Samples were powdered to 1–10 μm particle size. Magnesium, manganese and iron did not interfere. The effect of calcium carbonate was eliminated by the graphite addition. Results for copper (0.5–5 μg g^?1) in the scale and rocks agreed well with values obtained for dissolved samples. Relative standard deviations (n=10) were 4.9% for 1.2 μg g^?1 copper and 14.8% for 0.577 μg g^?1.     

Determination of cadmium,copper and lead in mineral coal using solid sampling graphite furnace atomic absorption spectrometry

Solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS) was investigated as a potential technique for the routine determination of trace elements in mineral coal and cadmium, copper and lead were chosen as the model elements. Cadmium and lead could be determined at their main resonance lines at 228.8 nm and 283.3 nm, respectively, but an alternate, less sensitive line had to be used for the determination of copper because of the high copper content in coal. No modifier was necessary for the determination of copper and calibration against aqueous standards provided sufficient accuracy of the results. For the determination of cadmium and lead two different modifiers were investigated, palladium and magnesium nitrates in solution, added on top of each sample aliquot before introduction into the atomizer tube, and ruthenium as a ‘permanent’ modifier. Both approaches gave comparable results, and it is believed that this is the first report about the successful use of a permanent chemical modifier in SS-GF AAS. Calibration against solid standards had to be used for the determination of cadmium and lead in order to obtain accurate values. The agreement between the values found by the proposed procedure and the certificate values for a number of coal reference materials was more than acceptable for routine purposes. The detection limits calculated for 1 mg of coal sample using the ‘zero mass response’ were 0.003 and 0.007 μg g⁻¹ for cadmium with the permanent modifier and the modifier solution, respectively, approximately 0.04 μg g⁻¹ for lead, and 0.014 μg g⁻¹ for copper.     

Metal ion distribution and solubility of Mn1−xCux(HCOO)2 · 2 H2O Mixed Crystals [1–5]

The metal ion distribution on the two metal sites of monoclinic Mn_1?xCu_x(HCOO)₂ · 2(H,D)₂O mixed crystals are studied by infrared and Raman spectroscopic methods. The spectral regions 3 200–3 400 cm^?1 (v_OH), 2 875–2 990 cm^?1 (v_CH), 2 330–2 500 cm^?1 (v_OD of matrix isolated HDO molecules), 1 350–1 400 cm^?1 (symmetric CO₂ stretching modes), 570–950 cm^?1 (H₂O librations), and 490 cm^?1 (M? O lattice modes) are mostly sensitive to the metal ions present. The frequency shifts of these bands with increasing content of copper show that Cu²⁺ prefers the M(1) site, coordinated by HCOO^? only. The strengths of the hydrogen bonds increase on going from manganese to copper formate, due to the increased synergetic effect of Cu²⁺. Solubility and X-ray data of the mixed crystals are included. Irrespective of the same crystal structure, two series of mixed crystals are formed: eutonic area at 0.65 ≥ x ≥ 0.5.     

Electrocatalytic Nitrite Reduction to Nitrogen Oxide by a Synthetic Analogue of the Active Site of Cu‐Containing Nitrite Reductase Incorporated in Nafion Film

The electrocatalytic reduction of nitrite to NO by [CuMe₂bpa(H₂O)(ClO₄)]⁺ ( 1 ), which is a model for the active site of copper‐containing nitrite reductase, incorporated in Nafion film was investigated. The Cu complex in the Nafion matrix exhibits an intense band at 267 nm and a broad band around 680 nm, assigned to d–d and ligand field transitions, respectively. The 77‐K EPR spectrum of 1 in the Nafion matrix reveals the typical axial signals (g_//=2.28, g =2.08, A_//=13.3 mT) of a tetragonal Cu²⁺ chromophore. The redox potential, which is related to the Cu⁺/Cu²⁺ couple, was ?146 mV (ΔE=72 mV) at pH 5.5. The redox reaction of 1 in Nafion was not dependent on pH and was a diffusion‐controlled process. The electronic structure and redox properties of 1 in the negatively charged polymer matrix were almost the same as those in aqueous solution. In the presence of nitrite, an increase in the cathodic current was observed in the cyclic voltammogram of 1 in the Nafion matrix. The current increase was dependent on the nitrite concentration and pH in solution. Upon reaching ?400 mV, a linear generation of NO was observed for the 1 /Nafion film coated electrode. The relationship between the rate of NO generation and the nitrite concentration in solution was analyzed with the Michaelis–Menten equation, where V_max=45.1 nM s^?1 and K_m=15.8 mM at pH 5.5. The Cu complex serves the function of both the catalyst and electron transport in the Nafion matrix. The sensitivity of the electrode was estimated to be 3.23 μA mM^?1 in the range of 0.1–0.4 mM nitrite.     

Electrochemical detection of blood lead based on the enhancement effect of copper

The anodic stripping peak current of lead on the glassy carbon electrode surface was greatly increased in the presence of high concentration of copper ion. The effects of supporting electrolyte, concentration of Cu²⁺, accumulation potential and accumulation time were studied on the stripping peak current of Pb²⁺. As a result, a sensitive, simple and rapid electrochemical method was developed for the detection of lead. In 0.01 M HNO₃ solution containing 800 g,g L^?1 Cu²⁺, the stripping peak current of Pb²⁺ increases linearly with its concentration over the range from 2 to 100 μg L^?1. The detection limit is 1 μg L^?1 after 4-min accumulation at ?0.8 V. It was used to detect the concentration of lead in blood samples, and the results consisted with the values that obtained by atomic absorption spectrometry.